1. Field of the Invention
The present invention relates to a functional member having a molecular layer on its surface and, more particularly, to a functional member having a molecular layer formed to coordinate on its surface, and a method of producing the same.
2. Description of the Related Art
Currently, as methods for formation of a molecular layer, there are known a so-called LB method and a chemical adsorption method (K. Ogawa et al., Langnuir, 6,851 (1990)).
The LB method is a method such that amphiphatic molecules developed on a water surface are collected together, with pressure being applied to the molecules in a direction parallel to the water surface, the molecules being then scooped onto a substrate while the pressure is kept constant, whereby a monomolecular layer is formed.
In the chemical adsorption method, a silane-based surface active agent is mainly used in such a way that the surface active agent is caused to go into condensation reaction with functional groups having active hydrogen, such as hydroxyl group and carboxyl group, which are present on the substrate, whereby a monomolecular layer of the silane-based surface active agent is formed on the substrate.
However, the above mentioned forming methods each have problems yet to be solved.
The LB method requires the provision of a developing bath first of all. The developing bath must be protected against vibration so that any slight vibration in the surroundings will not be transferred to the bath to cause the liquid surface to become wavy.
Another problem with the LB method is that since a molecular layer prepared by the LB method is fixed to the substrate by ionic bonding, the layer will be easily peeled off not only by a mechanical scratch, but also by being merely brought into contact with a liquid.
Whilst, the chemical adsorption method involves a problem that hydrogen chloride is produced because the silane-based surface active agent is brought into condensation reaction with a functional group having an active hydrogen atom as already mentioned. Therefore, the chemical adsorption method may be unsuitable for use with a substrate having low acid resistance.
Another problem with this method is that the silane-based surface active agent will not go into condensation reaction with a substrate having no active hydrogen atom; therefore, it is impossible to carry out layer-forming by using such a method.
The present invention has been developed in view of above mentioned state of the art and, therefore, it is an object of the invention to provide a method of forming on the surface of a substrate a molecular layer which involves no such problems mentioned above as have been encountered in the prior art.
It is another object of the invention to provide a novel functional material having a molecular layer firmly bonded to the surface of a component member.
Therefore, the present invention relates to a functional member having a molecular layer on its surface, wherein the molecular layer is a layer formed on the surface of the member through a coordinate bond, the coordinate bond being a multidentate bond such that at least one molecule is in bond with one metallic atom of the member, and such that two or more ligand atoms of the molecule are coordinated so that the metallic atom is placed between the ligand atoms. The invention also relates to a method of producing the functional member.
A multidentate bond wherein multidentate ligand molecules are in bond with atoms of a substrate metal is known as a chelate bond. A chelate bond is different from a covalent bond in the way in which the bond is formed, but the formed bond per se is same as the covalent bond. In a coordinate bond, both electrons that form the bond come from one of the atoms. Although the bond is covalent in character, a coordinate bond differs from a covalent bond in the origin of the electrons that form the bond. In a covalent bond, one electron originates on each of the two atoms being bonded. Therefore, the multidentate bond provides much higher layer/substrate metal bond strength than a monodentate bond, and accordingly the molecular layer formed can exhibit good performance characteristics, such as high heat resistance. Further, characteristic features of such multidentate ligand molecules can be advantageously utilized in providing the member with various properties, such as insulating property, electrical conductivity, permeability, bonding property, absorption characteristic, and protective property.
Multidentate ligand molecules usable for forming a molecular layer in the present invention include, for example, acetylacetone, acetoethyl acetate, benzoyl acetone, ethylenediamine, diethylenetriamine, triethylenetetramine, diethylamine, thiourea, diethanolamine, triethanolamine, iminodiacetic acid, nitrilotriacetic acid, ethylenediamine tetraacetic acid, quinoline-8-carboxylic acid, quinaldinic acid, o-aminobenzoic acid, oxalic acid, malonic acid, succinic acid, adipic acid, maleic acid, fumaric acid, anthranilic acid, 2-aminoperimidine, galloyl-gallic acid, potassium xanthate, oxine, cupferron, 4-chloro-3-methyl-5-nitrobenzene sulfonate, salicylaldehyde oxime, diantipyrylmethane, diethyl dithiocarbamic acid, p-dimethylamino benzylidene rhodamine, dimethylglyoxime, cinchonine, N-cinnamoyl-N-phenylhydroxylamine, thioacetoamide, thionalide, tetraphenyl borate, trimethylphenyl ammonium, 1-nitroso-2-naphthol, nitrone, neocupferron, bismuthyol II, p-hydroxyphenyl arsonic acid, 8-hydroxy-7-iodo-5-quinoline sulfonic acid, pyrogallol, 1-pyrrolidine carbodithioic acid, phenylarsonic acid,(phenylthio) dantinic acid, phenylfluoron, xcex1-furyldioxime, brucine, benzidine, N-benzoyl-N-phenylhydroxylamine, xcex1-benzoin oxime, benzo[f] quinoline, 2-mercaptobenzothiazole, rhodamine B, 4-tetradecyl-N-methyl salicylaldehyde oxime, 3-tetradecyl pyridine, itaconic acid, and pyromellitic acid.
For use as a component member on which a molecular layer is to be formed in accordance with the present invention, materials having a metallic portion or metallic oxide portion exposed on the surface are most suitable. The member may be in the form of a metallic plate or a material such that a metallic component is dispersed in resin and is contained as a part of the surface component. There is no particular limitation with respect to the configuration and size of the substrate.
In order to form a multidentate bond with a multidentatable molecule, it is necessary that the coordination number of atoms of the component metal should be two or more. Where the coordination number of such atoms is four or more, multidentate molecules which are in bond with one metallic atom may be two or more in number. For example, when the component metal is copper, the coordination number is 2 or 4; when the metal is nickel, the coordination number is 4 or 6; when cobalt, the coordination number is 4 or 6; when silver, the number is 2 or 4; if gold, the number is 4; when platinum, the number is 4 or 6; when aluminum, the number is 6; and in the case of tungsten, the number is 6 or 8.
To form a molecular layer on the surface of the component member, multidentate molecules may be brought into contact with the member. For causing such a molecule to contact the member, a suitable method is to bring the substrate into contact with one of a liquid molecule, a liquid solution having molecules dissolved in a solvent, and a gaseous molecule.
In particular, when a liquid solution is used, it is necessary to suitably select a solvent which will not affect the substrate on which a layer is to be formed. For example, water, alcohols, and ketones are most suitable for this purpose.
The variation of characteristics of a molecular layer and/or the control of molecular layer thickness may be adjusted depending on the kind of multidentate molecules and conditions used for causing the substrate into contact with the multidentate molecule.
In order to enable the formation of a strong chelate bond of the multidentate molecule with the component member to provide a molecular layer having high heat resistance, it is preferable that the molecule should be a molecule having not less than two functional groups selected from carboxyl groups, amino groups, and hydroxyl groups, including, for example, ethylenediamine, diethylenetriamine, triethylenetetramine, diethylamine, diethanolamine, triethanolamine, imino-diacetic acid, nitrilotriacetic acid, ethylenediamine-tetraacetic acid, quinoline-8-carboxylic acid, quinaldinic acid, o-aminobenzoic acid, oxalic acid, malonic acid, succinic acid, adipic acid, maleic acid, fumaric acid, anthranilic acid, galloyl-gallic acid, pyrogallol. By using such a multidentate molecule to form such a chelate bond of the molecule with the component member as represented by the formula (1) below is it possible to realize the formation of aforesaid molecular layer: 
(in which, M represents a metallic atom of the substrate).
The shorter the time for contact between the component member and the ligand molecule, and the lower the probability of such a contact, the smaller is the thickness of the molecular layer formed. Conversely, the longer the time for contact between the component member and the ligand molecule, and the higher the probability of such a contact, the larger is the thickness of the molecular layer formed. In order to form a multimolecular layer more efficiently and in sufficient thickness, it is desirable that a ligand molecule capable of dissolving the metal of the component member is preferably used.
In order to form a monomolecular layer, a component member is treated (immersed) in a ligand molecule solution having a concentration of the order of 0.1 mmol/L to 500 mmol/L under temperature conditions of more than the melting point but lower than boiling point of a solvent used and for not more than 24 hours, preferably at a temperature of 0 to 100xc2x0 C. for 1 to 60 minutes, more preferably at a temperature of room temperature (24xc2x0 C.) order for about 10 minutes, whereby a molecular layer comprised of a monomolecular layer can be formed on the surface of the component member.
Multidentate molecules which can be preferably used in forming such a monomolecular layer are exemplified by molecules comprising functional groups expressed by the following formula (2): 
In the formula (2), A1-A6 denote (CH2)nCOOH (n is 0-3), (CH2)nOH (n is 0-3), or (CH2)mNXY (m is 0-2; X and Y independently represent a hydrogen atom, a hydrocarbon group having not more than 8 carbon atoms, a phenyl group or an aromatic ring group having one or more hydrocarbon group having not more than 8 carbon atoms). The double bond in the formula (2) may be a part of a benzene ring or other aromatic ring.
Specifically preferred as such molecules are, for example, ethylene diamine, diethylene triamine, triethylene tetramine, diethyl amine, diethanol amine, triethanol amine, iminodiacetic acid, nitrilo-triacetic acid, ethylenediamine tetraacetic acid, o-aminobenzoic acid, oxalic acid, malonic acid, succinic acid, adipic acid, maleic acid, and fumaric acid. Among them, o-aminobenzoic acid is preferred.
When a monomolecular layer is formed, the use of a modified coordination molecule assures more accurate formation of the monomolecular layer because such a molecule is less liable to be influenced by manufacturing conditions. Usable as such molecules are, for example, anthranilic aid, itaconic acid, or pyromellitic acid, incorporating a substituent group which will not interact with metal, such as an alkyl group of the C3-C22 order, as expressed by the following formula (3): 
anthranilic acid or itaconic acid incorporating a fluoroalkyl group of the C1-C18 order which will not interact with metal, as expressed by the following formula (4): 
; or anthranilic acid or itaconic acid incorporating a bulky substituent such as a t-butyl group or a polycyclic aromatic group or the like, as expressed by the following formula (5): 
For forming a multimolecular layer, the ligand molecule solution is preferably treated under temperature conditions of more than the melting point but lower than boiling point of a solvent used and for a time period of 10 minutes to 48 hours, preferably at a temperature from room temperature to less than the boiling point for 10 minutes to 24 hours, more preferably at a temperature adjacent to room temperature for 10 to 40 minutes, whereby a molecular layer comprised of a multimolecular layer can be formed on the surface of the component member.
In the present invention, a molecular layer is formed on the surface of component member. This makes it possible to give a functional member provided on its surface with functional properties which coordinated molecules possess.
For example, it is possible to provide an electrically conductive component member with electrical insulating properties. If the conductive component member can be provided with electrical insulating properties on its surface in a molecular level thickness, it is possible to meet contemporary needs for size and thickness reduction with respect to electronic components. More especially, with respect to coils for transformers, motors and the like which take a particularly large part in volume and weight among various electronic components, size and thickness reduction is a current universal requirement yet to be met.
Generally, a coil is such that for securing the insulation between adjacent wires in the coil, the wires are coated with a resin material, such as enamel. The electromotive force of the coil is proportional to the number of turns of the winding. In order to increase the number of turns of the winding for a given volume, a high-performance winding machine has been employed to carry out high-density winding. However, since the thickness of resin material, such as enamel, used for coating the wires is so thick, i.e., on the order of 10 to 50 xcexcm, and since the electromotive force of the coil is proportional to the number of turns of the winding, attempts have been made to reduce the size of the coil and also to reduce the thickness of resin coating, such as of enamel, in order to increase the electromotive force of the coil. However, any further thickness reduction of the enamel coating has been found difficult because such thickness reduction would possibly lead to dielectric breakdown due to pin holes, and this has been a great hindrance to coil size reduction and/or electromotive force increase.
With the development of high-density packaging techniques for circuit boards, boards having adjacent conductors arranged in a very narrow spaced relation have been fabricated. In order to insure inter-wire insulation, it has been general practice that as the spacing between adjacent conductor electrodes becomes narrower, any conductor metal surface of the circuit board which requires protection from moisture is coated with a resin material, such as urethane resin or acrylic resin. However, in order to insure good insulation with respect to the circuit board, it has been necessary to coat the conductor metal surface of the board with a urethane resin, acrylic resin, or the like which has good moisture-proofing characteristics to a thickness of 100 xcexcm or more, or in some cases to a thickness of 10 mm or more. This has made it difficult to achieve size reduction and thickness reduction with respect to circuit boards.
The application of the present invention makes it possible to reduce the thickness of an insulating layer on a metal surface of coil wiring and/or of a circuit board, thus achieving a breakthrough size reduction and thickness reduction with respect to electronic components.
In this way, where the provision of a functional member having electrical insulation characteristics for use in electronic parts is intended, a water-insoluble and electrically insulative multidentate molecular layer is formed on the surface of an electrically conductive member to which insulation characteristics are to be imparted. The molecular layer so formed will not be elated by water even under high temperature conditions and will not be degraded in its insulating properties. The molecular layer is very thin because of a molecular level thickness. Therefore, a very thin insulating layer, which is far much thinner than any conventionally made insulating layer, can be formed on the surface of a conductive component.
Multidentate ligand molecules preferred for use in forming a water-insoluble and electrically insulative complex-molecular layer on the surface of a conductive component include, for example, anthranilic acid, 2-aminoperimidine, galloyl-gallic acid, potassium xanthate, oxine, quinaldinic acid, cupferron, 4-chloro-3-methyl-5-nitrobenzene sulfonate, salicylaldehyde oxime, diantipyrylmethane, diethyl dithiocarbamic acid, p-dimethylamino benzylidene rhodamine, dimethylglyoxime, oxalic acid, cinchonine, N-cinnamoyl-N-phenylhydroxylamine, thioacetoamide, thionalide, thiourea, tetraphenyl borate, trimethylphenyl ammonium, 1-nitroso-2-naphthol, nitrone, neocupferron, bismuthyol II, p-hydroxyphenyl arsonic acid, 8-hydroxy-7-iodo-5-quinoline sulfonic acid, pyrogallol, 1-pyrrolidine carbodithioic acid, phenylarsonic acid, phenylthiodantinic acid, phenylfluoron, a-furyldioxime, brucine, benzidine, N-benzoyl-N-phenylhydroxylamine, a-benzoin oxime, benzo[f] quinoline, 2-mercaptobenzothiazole, rhodamine B, and quinoline-8-carboxylic acid. Among these compounds, oxine, cupferron, oxalic acid, anthranilic acid, quinaldinic acid, and quinoline-8-carboxylic acid are preferred.
The multidentate ligand molecules preferably include at least a multidentate ligand molecule which can form on the surface of a conductive component a water-insoluble and electrically insulative complex molecular layer, and which can dissolve an oxide layer on the surface of the conductive component. This makes it possible to provide an insulation layer which is much thinner than any conventionally produced insulation layer and, in addition, is formed in uniform thickness. Usually, the metal surface has a spontaneous oxide layer formed thereon, so that there is low possibility of the metal itself being exposed on the surface. Multidentate ligand molecules will readily react with metal itself and metallic ions, but will not easily react with metal in oxidized condition. Therefore, the oxide layer is dissolved to cause metal exposure, and metal of the oxide layer are ionized to react with multidentate ligand molecules. It becomes possible to form a complex molecular layer to give a more uniform insulation layer.
Preferred multidentate ligand molecules which are capable of dissolving an oxide layer on the surface of a conductor material and forming a water-insoluble and electrically insulative complex molecular layer are exemplified by oxalic acid, anthranilic acid, galloyl-gallic acid, quinaldinic acid, quinoline-8-carboxylic acid, thiourea, pyrogallol, phenylfluorone, 4-chloro-3-methyl-5-nitrobenzene sulfonate, and Rhodamine B. Among of these compounds, oxalic acid, anthranilic acid, quinaldinic acid, and quinoline-8-carboxylic acid are preferred inter alia.
An oxide layer on the surface of a conductive material is made thicker by previously heat-treating the material. The use of a multidentate ligand molecule capable of dissolving an oxide layer as an insulation treatment agent can bring about an increase in the number of metallic ions which react with the multidentate ligand molecule. Therefore, the complex molecular layer becomes thicker in proportion to the thickness of the oxide layer. This correlation between the thickness of the oxide layer and the thickness of the complex molecular layer provides an advantage such that by selecting conditions for metal pretreatment it is possible to control the thickness of the insulating layer to be obtained.
When imparting electrically insulating characteristics to a conductive component, it is possible to control the thickness of the molecular layer to be formed within a thickness range of from a ultra-thin monomolecular layer level to the order of about 5 to 6 xcexcm by adjusting various conditions, such as temperature, treatment time period, and heat treatment. For example, a molecular layer of about 3 xcexcm in thickness can be formed under operating conditions of immersion for 10 to 40 minutes at room temperature and drying at 100xc2x0 C. for 30 minutes; and a molecular layer of about 5 xcexcm in thickness can be formed under operating conditions of prior heat treatment of the substrate at 100xc2x0 C. for 10 minutes, immersion at room temperature for 10 to 40 minutes, and drying at 100xc2x0 C. for 30 minutes.
When a copper wire for coil is used as conductive member in forming such an electrically insulating molecular layer, size reduction can be enhanced with respect to transformers, motors, and the like. At the same time, costs involved in moisture-proof coating and the like can be substantially reduced.
The present invention is applicable for use in circuit board insulation techniques by using as a solvent for insulation treatment a solvent which is not detrimental to resin material of circuit boards and the like. Further, when a circuit board with respect to which device soldering has been completed is immersed in an insulation treatment agent and then dried, only metallic portions of the circuit board, such as conductor metal, solder coating, and leads, are treated for insulation without involving such a problem as resin deterioration or the like. Therefore, the invention enables easy insulation treatment of circuit boards with soldered device.
When insulation treatment is intended, the solvent to be used is easy to dry after complex formation and not detrimental to the resin used for the circuit board. Therefore, suitable for use as such a solvent are water and at least one kind of material selected from the group consisting of monovalent alcohols having not more than 4 carbon atoms, such as ethyl alcohol, isopropyl alcohol, and butyl alcohol. A monovalent alcohol having 5 or more carbon atoms has a high boiling point. Such a monovalent alcohol is hard to evaporate during the process of insulation treatment, and therefore it remains on the metal surface after insulation treatment, which leads to poor insulating performance. Therefore, such a monovalent alcohol is not suitable for use. In the foregoing respect, the invention also substantially contributes toward size and thickness reduction of circuit boards and can substantially reduce costs which may otherwise be involved in moisture-proof coating, etc.
When 4-tetradecyl-N-methylsalicylaldehyde oxime, 3-tetradecyl bipyridine, 4-pentylanthranilic acid, 2-heptafluoroethynyl itaconic acid, or the like is used in forming a molecular layer on the surface of a component, water-repellent or rust-proofing characteristics can be imparted to the component.